set(model: , at : ) bug with zero index, added @discardableResult (CollectionSection/TableSection)

[wow-such-amazing]

Is it expected behaviour, that index should be greater than 0?

	public func set(model: ModelProtocol, at index: Int) -> ModelProtocol? {
		guard index > 0, index < self.models.count else { return nil }
		let oldModel = self.models[index]
		self.models[index] = model
		return oldModel
	}

[wow-such-amazing]

Also probably it should have @discardableResult?